Organic light Emitting Display (OLED) has a self-luminous, low driving voltage, high luminous efficiency, short response time, high definition and contrast, nearly 180° angle of view, wide operating temperature range, flexible display and large area full color display etc. advantages. The industry recognizes that the OLED as a display device with a most development potential.
OLEDs can be classified into two categories: a passive matrix OLED (PMOLED) and an active matrix OLED (AMOLED), or another two categories: a direct addressing and a thin film transistor array addressing. The AMOLED having multiple pixels arranged in a matrix is deemed as an active display type and is usually used as a high-definition large-size display device.
The OLED device generally includes: a substrate, an anode disposed on the substrate, a hole injection layer disposed on the anode, a hole transport layer disposed on the hole injection layer, a light emitting layer disposed on the hole transport layer, an electron transport layer disposed on the light emitting layer, an electron injection layer disposed on the electron transport layer, and a cathode disposed on the electron injection layer. The OLED device light-emitting principle is that the semiconductor materials and organic light-emitting materials are driven in the electric field by the carrier injection to recombine to light. In particular, the OLED device is usually used indium tin oxide (ITO) electrodes and metal electrodes, respectively, as an anode and cathode thereof. When the Anode and cathode are driven by a certain voltage, electrons and holes from the cathode and anode were injected into the electron transport layer and hole transport layer. The electrons and holes migrate through the electron transport layer and the hole transport layer to the light emitting layer, respectively, and meet in the light emitting layer to form excitons to excite light emitting molecules to emit a visible light by radiation relaxation.
Flexible OLED is an important research aspect of the OLED device. The OLED device in the light-emitting materials are usually polymer or organic small molecules, a material of the cathode is usually a low work function of active metals such as magnesium, aluminum etc. These luminescent materials and the material of the cathode are very sensitive to water vapor and oxygen, so a usage life of the OLED device is greatly reduced if the water and/or oxygen penetrate the OLED device. In order to achieve commercial requirements of the usage life and stability of the OLED device, packaging requirements of the OLED device are very strict. The usage life of the OLED device is usually at least 104 hours, the water vapor transmission rate is less than 10-6 g/m2/day, and the oxygen permeability is less than 10-6 cc/m2/day (1 atm), so the packaging is very important in the production of the OLED device and is also one of key factors affecting a product yield.
The conventional packaging technology includes: (1) a cover packaging technology: a UV curing dam or a dam and filling desiccant (Dam & Fill) coated on a packaging glass/metal is cured to provide a luminous device a relatively confined environment to block an entrance to which the water and oxygen permeate; and (2) a laser packaging technology: a glass glue coated on a packaging glass becomes glass powders after a solvent in the glass glue is evaporated, and after a vapor deposition substrate and the packaging cover are assembled, they are further bonded together by laser-melting the glass powders. The above conventional packaging technology can achieve a blocking effect of water/oxygen, but increases a thickness and weight of the device. It is not conducive for a production of the flexible OLED.
In recent years, the thin film encapsulation (TFE) technology is developed to overcome the drawbacks of conventional packaging technology, does not use the packaging cover and the dam to package the OLED device, and uses the thin film package to replace the conventional glass package. A large-size device package can be achieved and the device is light and thin. The so-called thin film package, that is, inorganic-organic alternating layers are formed on a surface of an OLED region of the substrate to block the water and oxygen by a thin film deposition. In the film packaging structure, the inorganic layer (the main component of silicon nitride, silicon oxide or aluminum oxide) is an effective barrier to water/oxygen, but some pinholes or particles defects are occurred in the production of the inorganic layer process; and the organic layer (including some polymer, silicon-containing organic matter, resin, etc.) is the role of covering the inorganic layer defects, and can release the stress between the inorganic layer to be flat.
As shown in FIG. 1, the conventional thin film package structure includes multiple inorganic layers 200 and multiple organic layers 300 alternately disposed on the OLED device 100. An area of the inorganic layer 200 is equal to that of the organic layer 300. The thin film packaging structure has an advantage of a simple according to claim process, so the deposition of the inorganic layer 200 can be completed by a single mask. However, the deposited inorganic layer 200 does not completely cover the organic layer 300 and the ends of the organic layer 300 are exposed in the air to form an entrance for water vapor. A packaging effect is damaged accordingly. Thus, another film packaging structure (shown in FIG. 2) is appeared and includes multiple inorganic layers 200′ and multiple organic layers 300″alternately arranged on the OLED device 100′. The area of the inorganic layer 200′ above the organic layer 300′ is larger than the area of the organic layer 300′ so that each of the organic layers 300′ can be completely covered with the inorganic layer 200′ thereon and the water vapor is not permeated inside the device through the organic layer 300′. However, since the areas of the inorganic layers 200′ are gradually increased from bottom to top of the OLED device 100′, so different masks are required to complete the deposition of the inorganic layers 200′. In the process, it needs to swap the mask for several times, so the process is complex and also easily introduces uncontrollable factors.